1. Field of the Invention
The present invention relates to an optical fiber composite ground wire, and more particularly, to an optical fiber composite ground wire by which the probability of breakage due to a difference in length between optical fibers in a tube can be reduced, and which can easily contain more optical fiber core wires without needing more special equipment.
2. Description of the Related Art
An electric wire line may be an underground line or an overhead line. In regions other than cities, an overhead line is usually used to transmit electricity. Since lightning can directly hit the overhead line, a wire, called an overhead ground wire, is installed along the uppermost portion of the line to serve as a lightning rod. Meanwhile, a communication line is needed for the electric line. In particular, communication lines for remote observation, remote control, etc. must be installed on an electric transmission line. An overhead ground wire and communication line can be installed separately, but they are preferably incorporated into one body.
However, a typical conductor such as copper or aluminum impedes the aforementioned incorporation, since a power line near a communication line hinders communication by inducing current. The communication trouble is proportional to the voltage and current of the power line, and is inversely proportional to the distance between the communication line and the power line. In particular, an electric transmission line carrying a high current at hundreds of thousands of volts causes a strong impediment to communications a communication line in its neighborhood. Nevertheless, it is inevitable to install the communication line on the electric transmission line.
In order to solve the above problem, an optical fiber composite ground wire (OPGW) has been developed. FIG. 1 is a cross-sectional view of a conventional optical fiber composite ground wire including a core 1 through which a plurality of channels are formed, a loose tube 3 inserted in the channel, and an external tension line 8 surrounding the core. At least one optical fiber 4 coated with acryl is housed in each loose tube 3. A gel-type filling material (not shown) for preventing entry of water fills the space between the optical fiber 4 and the loose tube 3 and surrounds the loose tube 3 in the channel 2. The external tension line 8 is comprised of a steel wire 6 for providing a strong tensile strength, and a coating 7 of highly conductive aluminum.
As shown in FIG. 1, the conventional optical fiber composite ground wire includes the external tension line 8 serving as an existing overhead ground wire, and the optical fiber 4 used as a communication path. In particular, the optical fiber greatly reduces the communication trouble compared to a communication line using an electrical signal.
However, in the optical fiber composite ground wire shown in FIG. 1, differences in the lengths of the optical fibers can cause them to break. The standard interval between power transmission steel towers is 600 meters. Accordingly, when the optical fiber composite ground wire is installed between the steel towers which are widely spaced, as described above, the optical fiber receives a strong tensile force due to its own weight. In this case, optical fibers receiving a relatively strong tensile force are likely to break, since they have significantly low elasticity and tensile strength, unlike the copper or aluminum used as the material of the typical power line. As shown in FIG. 1, if the optical fibers are irregularly inserted into the loose tube when the external tension line 8 and the core 1 stretch, some optical fibers are likely to receive a stronger tensile force than others. That is, even though the optical fibers are inserted giving consideration to the elongation of the entire overhead ground wire, some optical fibers may receive a strong tensile force.
Breakage of the optical fibers due to the above-described reasons is inevitable, and causes communication trouble. In particular, when the communication line is for remote observation or remote control of the power transmission line, great confusion may occur in the power transmission system, thus requiring an optical fiber composite ground wire more resistant to breakage of optical fibers.
Meanwhile, the loose tube usually contains 6 to 12 optical fibers. More than this number of optical fibers needs special equipment for assemble the optical fibers, which is expensive. An alternative to increasing the number of optical fibers in each tube is to increase the number of channels in the core 1. However, this weakens the overhead ground wire. On the other hand, if the outer diameter of the wire is enlarged, the safety of the steel tower deteriorates due to an increase in the weight of the wire.